In an automotive transmission, clutch assemblies are commonly used to transmit rotational motion or torque between two rotating members, such as an engine crankshaft and a transmission driveshaft. Standard friction-type clutch assemblies, or friction clutches, include a series of alternating friction and reaction plates that together make up a clutch pack, with the clutch pack being disposed within an outer clutch drum. The friction plate typically has a layer of rough friction material which is bonded or otherwise attached to the primary contact surfaces of a metal core plate, while the reaction plate typically has a relatively smooth contact surface configured to oppose the friction plate when the friction clutch is engaged. The friction clutch is engaged or applied using a controllable hydraulic force supplied by a transmission pump. The force actuates an apply mechanism, such as a clutch-apply piston, to selectively compress the friction and reaction plates of the clutch pack. Once compressed, the alternating plates become interlocked due to the friction forces imparted by the apply force and the friction material, thereby allowing the rotating members to rotate in unison.
Friction clutches may be of the dry-plate or wet-plate variety, with wet-plate friction clutches providing enhanced thermal performance due to the cooling qualities of the pressurized lubricating fluid. In particular, the enhanced thermal performance is accomplished by passing or directing the pressurized fluid, such as transmission fluid or oil, through and around the mating clutch surfaces to dissipate heat generated by the friction forces in proximity to the friction interface between the surfaces. Lubricated surface cooling of friction clutch plates is often provided via a series of shallow radial channels or grooves along the contact surfaces of the friction plates, with the grooves being pressed into or formed on a separate bonded friction material layer, or defined by the gaps between discrete patches of friction material. However, as such patches and/or surface grooves reduce the total contact area between the mating clutch surfaces, surface temperature may increase along the remaining contact surfaces, resulting in less than optimum overall plate cooling. Also, spin losses may occur while the clutch assembly is disengaged as friction forces create drag between the plates.